This invention relates to a hindered-settling fluid classifier applicable for wet processing aggregate, such as sand, coal, gravel, and ash. The invention effectively washes and classifies raw material based on its specific gravity and settling velocity. The resulting processed aggregates are commonly found in everyday items, such as paint, paper, plastics and glass, and are often used as mineral supplements for agriculture, medicines and household products.
As a result of higher quality demands and an increased use of fines, washing has become a common and necessary step in aggregate processing. Some asphalt and other sand specifications allow for greater use of fines. On-going studies by the Georgia and North Carolina transportation departments, along with the International Center for Aggregates Research, have shown high-fines mixes to be as good or better for strength and durability as many current sand specifications. As this research proves out, specifications have and will continue to change for higher-fines use. As this happens, aggregate processing plants will need to be updated or built to retain more fines.
Presently, the aggregate industry uses material-recovery systems including cyclones and sand dewatering screws to process and recover fines. Cyclones are generally expensive, and require sump tanks, high-horsepower pumps, and extensive plumbing within the processing plant. Sand-dewatering screws are a generally cost effective alternative, but have several disadvantages and limitations. Sand screws receive a quantity of slurry directly from a wet screening operation or from a classifying tank. The screw then augers out the sand product to a minimum moisture content to be conveyed and stockpiled. The resulting product is a single processed aggregate ranging in size from the largest feed to the cut-off point of fines removal. In many cases, the processed aggregate is relatively “dirty” (includes deleterious particles) and does not satisfy growing demands for high-fines usage.